Acoustic sounding apparatus



2 Shee Filed Aug. 27, 1927 NOV. 3, 1931. A, BEHM 1,830,254

ACOUSTIC SOUNDING APPARATUS I Filed Aug. 27, 1927 2 Sheets-Sheet 2 -3 Fig.5

t E 5 Q .9 f o 2 g 13 o 3 #7 17 D @1 A'A'A'A'A g k Fig.4

Patented ov. 3, 1931 PAT NT; OFFICE ALEXANDER BEHM, OF KIEL, GERMANY ACOUSTIC SCTUNDIN'G APPARATUS Application filed August 27, 1927, Serial No. 215,941 and in Germany August 28, 1926.

The invention relates to apparatus for depth sounding by the acoustic method, that is to say by timing the interval betweenthe emission of a sound and the reception of the echo, and computing the distance from the time observed. This method may be used both at sea and for purposes "of aerial navigation.

In deep water, and at great heights above 11! dry land, soundings taken at long intervals are generally adequate, but in shoal water, and when flying low a more rapid sequence of soundings becomes necessary. Moreover when sounding in very shallow water, or

from low flying altitudes, as for instance, during the landing of an air-craft, there is need for the greatest accuracy and the results must be clearly indicated with great promptitude. The object of my invention is to provide an acoustic sounding apparatus which meets these requirements. My device embodies an adjustment which makes it highly accurate and efficient at all altitudes.

' An embodiment of the invention is shown in Figs. 1,2 and 3 of the accompanying drawings, certain electrical connections and arrangements being shown diagrammatically in Figs. 4 and 4a. Fig. 5 shows a detail which is explained further on.

Within a casing 1 (Fig. 1) there is an easily rotatable disc 2, having a vane 3 which constitutes the armature of an electromagnet 4.

A second vane 5 on the disc 2 is adapted to abut against a spring 6 which is secured to a holder 7 within the casing. The holder 7 carries an arm 8, which is provided with a nose 9 adapted to engage notches 11 and 12 in a cam 10. The cam has a handle 13, which is movable in a slot in the casing 1, through which it protrudes. A spring 15 holds the nose 9 in engagement with either of the notches 11 and 12. These notches are at different distances from the aXle 14 of the cam. When the cam is rotated clockwise by means of the handle 13 the nose 9 slides out of the notch 11 and into the notch 12, and the tension of spring 6 is lessened somewhat, and when the cam is rotated in the reverse direc tion the spring is restored to its former tension. It is thus possible, by means of the spring, to impart to the disc 2 rotation at two different speeds. In order to increase the range of the measurement, I may provide three notches, instead of two, but this necessitates the provision of a third scale. The arm 8 controls an electric contact device 45, 46, the purpose of which will be explained further on.

Mounted on the axle of the disc 2 is a partially toothed spur wheel 16, with which a toothed segment 17 of larger diameter is engaged. This toothed segment is on an axle 18 rotatable within the casing, and is balanced by means of a counter Weight. There is also attached to the axle 18 a mirror 19, which also rotates with the toothed segment 17 In order to restore the gears 16 and 17 and the disc to their original positions, two hair springs 29 and-30 are provided, which are attached to fixed holders at one end and to the disc 2 and to the toothed segment 17 respectively at the other end. They areplaced under stress when the disc is rotated in the direction indicated by the arrow.

IVhen in the zero position shown in Fig. 1, the mirror 19 is so placed that array of light issuing from a small lamp 21 (for example, the bulb of an electric pocket lamp), after passing through a small, screened spherical lens 23 ands. mircroscopic magnifying lens 24, is r'fl ected by the mirror and produces a bright spot of light 26 at the zero point of a scale 25. Since the spherical lens 23 is of very short focal length, the image 26 of the lamp filament appears to the eye of the observer, even after the strong magnification by the lens 24, as a very intensive pin point of light, which remains plainly visible on the screen during the rapid movement set up when taking soundings. The screen carrying the scale 26 is curved cylindrically around the axle 18 of the mirror, so that the spot of light 26 is of uniform size and'intensity at all parts of the scale and does not become distorted. For making the screen I prefer to clamp a strip of thin tracing paper between two transparent strips of celluloid of the same size as the screen. A screen made in this way can be bent very accurately into cylindrical shape, and is not sensitive to shocks; it also has the advantage, over ground glass, that it produces a stronger dispersion of light, with uniform illumination of all portions of the scale, facilitating accurate reading. The lamp 21 is screwed into a holder which, in order that the lamp may be easily replaced, is slid into a sleeve in the casing, from which it can be easily withdrawn from the outside, after unscrewing the joint 22. The spherical lens 23 is placed on the end of a needle-like glass or metal rod forming a continuation of a leaf spring 27, which is freely movable between the poles of an electromagnet 28. In the zero position of the apparatus the magnet 28 is energized by current and the spring 27 is slightly stressed.

When no current flows through the coils of the magnet 28 the spring 27 is released and the spherical lens at the end of the leaf spring 27 is strongly deflected, and commences to Vibrate. Corresponding vibration is thus imparted to the point of light 26 on to the screen, the vibrations being transverse to the scale 25.

In Fig. 2, which is a top plan view of the sounding apparatus, looking on to the curved scale, the scale is seen on the right, this being the scale used for small altitudes and depths, with the disc 2 rotating rapidly and the nose 9 engaged with the notch 11 of the cam 10. On the left there is the scale 33 for greater altitudes and depths, when the disc 2 rotates slowly, the nose 9 being engaged with the notch 12 of the cam 10. Below the scales is a nut 22 for changing the lamp 21, the handle lever 13 for regulating the speed of the disc, and hinged bearing-s 31 for the ends of the axle-14 of the cam these ends forming a swivel, on which the whole casing can be tipped, (see also Fig. 3). By tipping the apparatus it is possible to view the entire range of the scale and notwithstanding the curvature to take readings equally well on all portions of the scale.

Fig. 3 is a side view of the instrument to a smaller scale. This figure shows more particularly the method 0 mounting the sounding apparatus 011 an instrument board 32.

In order to protect the apparatus against shocks it is suspended by means of a spring 34 from a bow shaped support provided with holes, a second spring 35 from the instrument board being attached from below to the case 1. To obtain the oblique position most favourable for reading the scale the spring 34 can be hooked into a higher or lower hole in the support 33. An arched guide 36, having a stop at its end, prevents the apparatus from tipping over too much. Countersinking the apparatus in the board affords a certain protection of the screen against outside light.

In addition to this, however, a hood 38 of cloth or the like may beprovided, and when the instrument is in 'use this hood can be stretched out by means of a strut 39. The cable for the light is marked 37.

In order to thoroughly explain the arrangement and the operation of the sounding apparatus I will now refer to the connections shown in Fig. 4. In this diagram the parts already described are designated by the reference characters already used. On commencing. to take a sounding the parts are in the positions shown in Figs. 1 and 4. The spring 6 is taut against the vane 5 of the disc 2. The disc 2 is, however, kept at rest, since the magnet 4, energized by the battery 40, is attracting the vane 3. The circuit from the battery 40 is through the following path conductor a, contacts 41 and 42, conductors Z), c, d and 6, contacts 43 and 44, conductors f and g, contacts 45 and 46, rheostat 47, microphone Ma, conductor it, magnet coil 2', conductors k and Z, and back to the battery. The strength of the current energizing the magnet 4 is so regulated with the aid of the rheostat 47 that it only very slightly exceeds the power of the spring 6, so that even a very slight weakening of the current atonce causes the disc '2 to be released. In the positionpf rest the lamp 21 is in the circuit composed of the battery 40, conductor a, contacts 41 and 42, conductors b and s, resistance 53, lamp 21, and conductor t. When the sounding signal is emitted the microphone. Ma, which is arranged in immediate proximity to the sound emitter (not shown), is affected by the sound waves, and its resistance, is momentarily substantially increased, so that the current energizing the magnet 4 is temporarily weakened. Consequently during the period of the detonation the power of the spring 6 exceeds that of the magnet 4, and the disc 2 is rotated in the direction indicated by the arrow. In the absence of means for preventing it the current would again flow with full strength through the coils of the magnet 4 as soon as the weakening due to the microphone has ceased, and the armature 3 would then again be attracted by the magnet 4. A short movement of the disc 2 and the relaxing of the spring 6 are, however, sufficient to open the contact 43, 44 (see Fig. 4a) and thus to interrupt completely, though temporarily, the current flowing around the magnet 4. Thus the disc 2 owing to the effect of the powerful impulse imparted to it by the spring 6, continues to rotate in the direction indicated by. the arrow marked as. The rotation of the disc is transmitted at reduced speed to the toothed segment 17 and the mirror 19, so'that the point of light 26 reflected from the mirror 19 moves upwards on the scale 25.

When the disc 2 has covered a certain distance, a third vane 48 on the disc strikes the end of a contact spring 49 projecting into. its path, whereby the contact between the spring 49 and an adjustable screw 50 is temporarily opened. The contacts 49, 50, are in the cirasaoaee cuit: battery 40, conductor a, contacts 41 and 42, relay magnet coil 51, conductors m, n and 0, contacts 49 and 50, conductors p, g and 1' leading back to the battery. Thus, when the contacts 49 and 50 are separated, no current will flow through the coils of the relay magnet 51. The contact spring 41, which is a magnet armature and abuts against the relay magnet 51, is thereby released and springs.

back into its position of rest, whereby the contacts 41 and 42 are separated. Consequently- 49, which is again stressed, the hair springs 29 and 30, which are likewise stressed again, also rendering assistance. When the armature 3 on the disc 2 again comes within range of the pull of the magnet 4, the parts are returned to their starting position shown in Figs. 1 and 4. The contacts 49 and 50. are then in closed position, as well as contacts 43 and 44. The consequence of closing the contacts 49 and 50, is that the relay magnet 51 (in circuit :-battery 40, conductor a, contacts 41 and 52, conductors s and h, microphone Ma, rheostat 47, contacts 46 and 45, conductors g and f, contacts 44 and 43, conductors c, d, c and b, coil 51, conductors mfn and 0, contacts 49 and 50, conductors p, g and 9 leading back to the battery) again receives current and again attracts its parmature 41. The contacts 41 and 52 are thusseparated and the contacts 41 and 42 closed. This causes the lamp 21. to lightagain and the current supplied to the magnet 4 to be weakened. The attractive force of the latter then only very slightly exceeds the strength of the spring 6.

It will be seen that when the disc has completed a to and fro movement the following operations have been carried out :-An acoustic signal has been given, with lamp 21 burning, this is followed by increase of resistance in the microphone Ma and temporary weakening of the magnet 4, release of the disc 2 and separating of the contacts 43 and 44; rotation of the disc 2 in the direction indicated by the arrow m; opening of contacts 49 and 50' by vane 48; deenergizing of relay magnet 51; opening of contacts 41, 42 and closing of contacts 41, 52; extinguishing of lamp; in-

' crease of strength of magnet4; rotation of the disc 12 in reverse direction by the spring 49,

with-the aid of the hair springs 29, 30; re-

newed attraction for the armature 3 by the magnet 4; closing of the contacts 49, 50 and 43, 44; return of all parts to the starting position, and relighting of lam 21.

The spot of light reflecte by'the mirror 19 and projected on to the scale produces during these operations a single streak of light emanating from 26 and running parallel to the scale 25, the light being extinguished at the moment of the reversal of the disc movement. The return of the disc 2 is not visible on the screen, and the point of light does not reappear at the zero point on the scale until the lamp 21 is again alight. These operations are repeated as often as the magnet 4 is deprived of current, even if this occurs several times in one second.

When the echo reflected from the sea bottom or dry land arrives, the sound wave affects a microphone Me arranged in a suitable position, in the following circuit battery 40, conductor u, microphone Me, rheo stat 54, conductor a, magnet coil 28, conductors w and 2 leading back to battery. Microphone Me is only actuated upon the reception of the echo, it being shielded or cut out in any one of the well known ways so that it is not aflected upon the issuance of the initial sound. The resistance of the microphone is suddenly increased considerably and the attractive power of the magnet 28 is correspondingly weakened. The spring 27 located in the magnetic field is consequently released, and the lens at its end makes an abrupt lateral movement transversely of the normal direction of travel of the spot of light 26. This movement is indicated in Fig. 2 bythe horizontal line a-B, and the height at which it occurs can be read on either of the scales 25 and 33. Since after cessation of the echo the magnet 28 again acquires its full attractive force the lens 23 performs a few oscillations (see Fig. 2) and the streak of light then rapidly approaches to its original path, terminating at 8. During the return movement of the disc the lamp 21 does not burn, as explained above, but the impression of the streak of light remains for some time upon the ret ina ofthe observer, in the form of a sharply defined graph against a dark background, so that a quick and accurate reading of the height or depth at which the signal was given is obtained.

Since with decreasing depths the intensity of the echo, and its effect upon the receiver, quickly increase, the horizontal deflections of the spot of light tend to increase in length as the altitude or depth decreases. The length of the path a-B may, for example, at an altitude of 1 meter already amount to about 20 millimeters. This is particularly important for taking readings during the landing of a flying machine.

In the foregoing description of the action of the apparatus I have assumed that the nose 9 is in engagement with the notch 11 of the cam. The spring 6 is thus placed under considerable tension, and the disc 2 makes a very rapid rotary movement The scale 25 has large divisions for readings suitable for this setting, but for large altitudes and depths the cam is rotated by means of the lever 13, so that the nose 9 engages the notch of the cam 10, and the spring 6 is somewhat relaxed. The disc 2 then receives a weaker impulse and rotates. more slowly. Under these 'circum stances provision, must be made. to ensure that the ,weakening of the electromagnet 4, will actually enable the spring to propel the" disc. L I v For this purpose, when the cam 10 is rotated the arm 8 opens the spring contacts 45, 46 and cuts in aresistance 55. i i

The provision of a transmission gear between the oscillating disc and the light projector renders the use of two scales-practicable for the first time for the following reasons. If the mirror 19 were fixed to the axle of the disc 2, it would still be possible to provide for diflerent speeds of rotation, but difficulties would arise in connection with the scale. It the scale divisions were made such that clear readings could be obtained for small altitudes and depths, the scale would be much too large for the measurement of large altitudes and depths. If, on the other hand, the scale were calibrated for large distances, so that it might be used conveniently with the disc making a slow movement, the divisions of the scalewould be too small for accurate readings of small altitudes and depths. Moreover, the slowing down of the disc movement is limited in practice, as the disc must be given a certain margin of kinetic energy for overcoming friction.

The use of the transmission gear has the further advantage, in connection with aerial navigation, that in case of sudden danger of contact with the earth, as for' example when flying in fog over mountainous country, the pilot can obtain at once a direct reading of his altitude, because thewscale for low altitudes also starts at zero and is'not, as is the case with some instruments, only a, continuation of the scale for large altitudes.

Another advantage of the improved sounding apparatus is that it is possible to ascertain from'the length ot the lateral deflection of the light rays whether the signal given was of the right intensity and whether it was sufliciently sharp. In the case of sounding apparatus where the oscillating disc is braked at the end of the measurement this is not the case, because the action of the brake occurs in exactly the same way with weak and; strong signals. If I use a sound receirver',' whose response is nearly proportional to the strength of the echo, I may arrange in addi-' tion to the altitude or depth scale, a scale perpendicular thereto, with the same zero mark, as shown in Fig. 5. From various points on this scale I may draw curves J L, J each indicating the deflections obtained at difler'ent altitudes by reflection of the sound from ground of a particular kind, say dry land, water, or snow. If the amplitudeof the deflections-is carefully observed, with reference to these curves the pilot will be able, with some little practice, to ascertain with tolerable accuracy the nature of the country overv which he is flying. The said curves are preferably marked in different colours. In Fig. 5 they are difierentiated by being drawn respectively in a full line, dash lineand dotted line. Curves of this kind may be provided for ice, tilled soil, tree tops and so on. It is of course, for the accurate use of these curves essential that the strength of the sound waves sent out be always the same. In order to be able to ascertainwhether the signals are in fact uniform I may provide, as shown in Fig. 5, below and parallel with the intensity scale, a special scale whose divisions correspond with. the sound intensity of the reflector and on which a special sound intensity measurer indicates the intensity of the reflected sound at each the case of aircraft, it has been found very' convenient to arrange the zero point of the altitude scale at the lower end of the same, because the horizontal deflection 'u-B which, when landing, drops gradually to a certain extent corresponds to the descent of the machine. iIn order further to enhance'this impression I may, as shown in Fig. 5, difl'erentiate the part of the scale-window below the zero line, by dashes or by colouring, to represent in the case of ships, the sea bottom,and in the case of aircraft the earth; it is preferable to make the projection plane at this point opaque and to provide a window at the zero position.

If it is desired to obtain the readings with a particularly intense light, a further contact may be introduced between the contacts 43, 44 and 49, 50, this contact being held open in the position of rest by the vane 5 on the disc 2, so that the lamp resistance 53 becomes impression of the luminous curve upon the observers eye can be intensified and the readmg of the sounded depths and heights further facilitated.

Owing to the coincidence of the zero position of the luminous point with the zero point of the scale. a single maximum deflection of the luminous streak is clearly perceptible,

so that no confusion is likely to arise, even in the case of inexperienced observers. The distinctncss of the reading is further increased by the fact that the part of the luminous curve lying above the horizontal deflection appears,

with its constantly diminishing oscillations, in the form of a lightly hatched surface, which emphasizes the horizontal stroke aB.

What I claim as my invention and desire to secure by Letters Patent of the United States 1S In an indicating apparatus of the kind described, a rotatable body, a spring adapted when released to rotate said body, means for releasing said spring, an arm fast on said spring. a cam having a plurality of different sized notches. each notch adapted to engage said arm for imposing different stresses on said spring, and means for adjusting said cam.

: In witness whereof I have signed this specification.

ALEXANDER BEHMi 

